U.S. Patent Application Publication No. 2002/0147534 describes an object sensing system having a plurality of FCWM sensors that determine the position of the object by triangulation. The same thing is described in U.S. Pat. No. 5,872,536. PCT International Published Patent Application No. WO 00/08484 describes a parking aid having a plurality of ultrasonic distance sensors. The latter are operated at different transmitting frequencies and are equipped with bandpass filters to prevent superimposition of the signals.
U.S. Patent Application Publication No. 2002/0075178 describes an FCWM radar transmitter having a local voltage-controlled oscillator. An emitted radar signal is modified as to its frequency, and the beat between a back-reflected and an emitted signal is sensed and is evaluated as the transit time of the reflected signal. The article “A 24-GHz Short Range Radar Network for Automotive Applications” by Michael Klotz and Hermann Rohling, which appeared in 2001 in CIE International Conference on Proceedings from 15 to 18 October, describes a pulsed radar technology for controlling a vehicle in road traffic.
The article “Waveform Design Principles for Automotive Radar Systems” by Rohling et al., CIE International Conference on Proceedings on Oct. 15-18, 2001, Piscataway, N.J., USA, describes a 77-GHz FMCW radar sensor for automobile applications.
PCT International Publication Patent Application No. WO 01/26183 describes an asymmetrical multi-beam radar sensor having an angle evaluation system that has polyrods.
Increasing the safety and convenience of vehicles is one of the primary goals of the automobile industry. One possibility for enhancing the safety of a vehicle involves automatically detecting road traffic obstacles. This requires a determination of the vehicle's distance from a possible obstacle, as well as a determination of the direction in which the obstacle is located. The direction to the obstacle must be determined, inter alia, in order to distinguish between obstacles that are located on the road or at the side of the road.
One possibility for enhancing vehicle convenience involves determining the speed of a preceding vehicle in heavy traffic, and automatically adapting the speed of the own vehicle. This means that it must be possible to determine the distance to the preceding vehicle, its speed, and whether that vehicle is located in the same lane, or at an offset from the own vehicle in a second lane. These are two possible uses for a radar system in the vehicle sector; another might include, among others, a parking aid. All these methods require an apparatus that allows the distance and direction of an object with respect to the vehicle to be determined.
In a conventional method, a primary source for microwaves is made available, the emission of which source is collimated with the aid of a suitable optical system into a beam having a half-power width of 3-4°; and then, by a deflecting optical system, forms three to four beams therefrom which together cover a relatively narrow angle range of 8 to 16°. For each individual one of these beams, the portions reflected from an object are separately sensed with a sensing device. An amplitude comparison of the reflected portions for the individual beams makes possible a determination of the direction in which the object is located. The achievable angular resolution, as well as the angle range covered, are disadvantageously defined by the mechanical configuration, and thus limit the field of application of the sensor.
A further method provides for determining, from the phase of the reflected beams, the geometrical placement of the object with respect to a sensor assemblage. A sensor assemblage provides for a suitable transmitting device to illuminate the entire desired observation region, and a plurality of receiving devices sense the signals reflected from the object. The receiving devices determine the phase of the individual reflected signals, and a signal processing device calculates, on the basis of those phase signals, the different path lengths that the reflected signals have traveled, and thus the geometrical placement of the object with respect to the vehicle. A disadvantage of this assemblage is that a high output power is required for the transmitting device, since part of the transmitted signal must be made available, for all receiving directions, for a receiving mixer, and large losses in the requisite distributor networks occur because of the strong damping in the frequencies used, in the region of 76-81, 122-123, or 126-150 GHz (or even higher).
A further sensor assemblage provides for the use of only one receiver device, and for the latter to be connected, sequentially in time, to a plurality of antenna devices. The disadvantage of this apparatus is that the duration of a measurement using all the antenna devices is too long, because of the multiplexing method, to allow this apparatus to be used for dynamic situations in road traffic.
A further sensor assemblage provides for combining the receiving device with the receiving device, and for connecting them, successively in time, to a plurality of antenna devices. This apparatus likewise has the disadvantage of too long a measurement time.